Various types of intraocular lenses (IOLs) are known. For example, there are known one-piece intraocular lenses and composite intraocular lens having multiple pieces. A one-piece intraocular lens is one where both optic and non-optic portions are made from one material. The non-optic portions of IOLs are referred to as haptic portions, and are used for attachment purposes. Two general designs for the haptics are a “plate-type” and a “C-haptic” type, both of which may have a variety of shapes. A plate design is shown in FIGS. 1A and 1B. A “C” design is shown in FIGS. 2A and 2B. These Figures are discussed in more detail below.
It is desired that the length of incision needed to insert the intraocular lens into the eye be reduced. Reducing the length of the incision requires the use of a very soft material for the lens. The material should be soft enough to permit the lens to be folded, inserted through the incision, and released. Thus, intraocular lenses are preferably foldable so that they can be easily inserted into the eye. Approaches to achieve foldable materials include the use of lenses formed of hydrophobic silicone-polymers, certain hydrophilic 2-HEMA homopolymers, and composites of a hydrophilic optical core with hydrophobic poly(methyl)methacrylate (p-MMA) based haptics.
IOLs with mechanically-attached haptics are lenses where the optic-portion and the haptic-portion are made separately, usually from different materials, and attached. For example, the lens portion can be made of a hydrogel or silicone-based material and the C-shape haptics from a rigid material like p-MMA, polyvinylidene fluoride (PVDF), and polysulfones. The p-MMA haptics are attached to holes drilled into the optic portion.
Although P-MMA is the traditional hydrophobic intraocular lens it is not easily foldable and requires a relatively large incision for insertion. To make hydrophobic materials foldable, rubber-like materials, such as silicone derivatives, have been included in the rigid polymer matrix or materials consisting primarily of silicone derivatives have been used. Although the softness of a primarily silicone material is ideal for folding prior to insertion, when the lens and its haptics unfold in the eye, the almost gel-like softness of the lens makes it difficult for a surgeon to properly position the lens in the eye. Furthermore, the silicone lens often does not provide sufficient rigidity for the lens after insertion and the combination of deformation from compressive forces along with lens movement can produce lens distortion and compromise the optical integrity of the lens.
Because of its inherent properties, p-hydroxyethyl methacrylate (a homopolymer of HEMA) has been used as a foldable material for intraocular lenses. However, the low refractive index of p-HEMA when hydrated leads to limitations in the optical center design and a compromise between its folding ability and its optical requirements.
One of the limitations of one-piece P-HEMA hydrogel lenses has been that the haptic portion lacks the desired modulus and can compromise lens positioning. To address this issue, polymer materials have been combined to give a soft, foldable intraocular composite lens such as P-HEMA or other soft acrylic material for the optic zone, and a rigid structure around the outside of the lens, made from a hard plastic such as P-MMA. See U.S. Pat. No. 4,718,906 and U.S. Pat. No. 5,326,506, both hereby incorporated by reference in their entireties, which describe composite intraocular lenses. These multicomponent materials are made by embedding one material in the other, by concurrent extrusion processes, by solidifying the hard material about the soft material, or by forming an interpenetrating network of the rigid component into a preformed hydrophilic core.
U.S. Pat. No. 5,326,506, discloses a composite intraocular lens including a soft, pliable inner lens optic using rigid haptics. The lens optic material is a low water content material such as a copolymer of 2-HEMA and hydroxy hexylmethacrylate which has a high refractive index due to its low water content. The hard, yet foldable, P-MMA haptics, are attached by an interpenetrating network.
U.S. Pat. No. 4,764,169, hereby incorporated by reference in its entirety, discloses a composite intraocular lens including a small, hard inner lens optic and a soft, pliable skirt surrounding the lens optic. The lens optic material is a relatively hard material such as P-MMA, polysulfone, or polycarbonate. The soft, pliable skirt is a silicone, hydrogel, or like material.